1. Field of the Invention
The present invention relates to a constant-quality rate control technique and, more particularly, to a constant-quality rate control system and algorithm for regions of interest in a single video source.
2. Description of Related Art
Bit rate control plays a very important role in video quality. Control mechanisms are used to determine the data rate of compressed video so that video streams can be successfully delivered and the best video quality can be achieved.
According to the bit-rate characteristics of the compressed video, rate control can be either constant bit-rate (CBR) or variable bit-rate (VBR). CBR is widely used in digital A/V applications that are constrained by constant channel bandwidth such as digital television or video conferencing. However, because video signals are non-stationary in nature, it is almost impossible to achieve constant video quality with CBR encoding. Alternatively, VBR is often used since it can provide constant video quality.
There are many constant-quality rate control algorithms that have been developed. Adaptive algorithms vary the quantization step size according to characteristics or properties of a video sequence. These algorithms however cannot guarantee meeting storage size constraints. Two-pass algorithms generate constant-quality video during the second pass of the encoding process according to information obtained in the first pass.
However, while these algorithms can perform effectively in certain applications, they cannot be used in real-time applications due to the computational complexity and two-pass nature of the two-pass algorithm.
To solve the above problems, several single-pass constant-quality rate control algorithms have been developed in which the quantization parameter for a frame is selected according to the statistics gathered from characteristics of previously encoded frames.
Therefore, there is need for a constant-quality rate control algorithm which provides optimal overall quality of a video signal while meeting the bit-rate constraint.